1. Field of the Invention
The invention relates to a control circuit for an electric-motor-operated window lifter drive of a motor vehicle, having a first and a second switch for opening and, respectively, closing a vehicle window, as well as having a control device, which, when the switches are activated, actuates the window lifter drive, and having a device for detecting inundation of the vehicle.
2. Description of the Related Art
A window lifter drive which is also referred to below as a window lifter and which is used to lift (close) and lower (open) a vehicle window in a motor vehicle usually comprises an electric motor which is generally coupled via a transmission gearing to the vehicle window and is actuated by means of an electronic control unit. For this purpose, a control device supplies pulses or signals to a relay circuit in the form of two individual relays or a double relay in order to energize the electric motor in opposing directions and therefore drive the electric motor in opposing directions of rotation. In addition to or instead of relays it is also possible to use power semiconductors, for example four MOSFETs in a bridge circuit.
The electric-motor-operated drive is usually actuated by means of switches or pushbutton keys which are accessible to an operator in the motor vehicle for the vehicle window which is to be respectively moved. After the activation of the respective switch or pushbutton key, the control device is actuated in order to move the vehicle window into the open position or closed position. The control signals which are generated by the respective switches can be conducted in the form of high levels and low levels or changes in level to inputs of the control device, which is generally embodied as a microcontroller or comprises a microcontroller.
Undefined states or levels at the signal inputs of the control device are problematic here, with the result that a correct interpretation is not ensured. Undefined states occur, in particular, if moisture and, in particular, water penetrates the switch system which comprises the switching contacts of the switches or pushbutton keys for lifting and lowering the vehicle window.
In particular when the vehicle is immersed in body of water, the vehicle and therefore the control circuit are inundated. Undefined level states which are caused as a result of this and which result from short-circuits can lead to the vehicle window no longer being able to be opened in order to permit the vehicle occupants to use the window to exit from the vehicle which has been involved in an accident.
In order to counter this problem and to ensure reliable opening of the respective vehicle window even in a vehicle which has been inundated, for example German patent DE 100 28 490 A1 discloses generating an inundation signal, by means of an additional indundation detector circuit, if the vehicle is inundated. Such a detector signal causes the energy supply to the relay which is responsible for the movement of the window pane in the closing direction to be interrupted, with the result that the vehicle window can then only be driven into the open position. A similar control circuit with an additional immersion opening switch is known, for example, from German patent DE 601 11 665 T2.
U.S. Pat. No. 6,690,131 (EP 1 207 261 A1) discloses a circuit with a wetness detector which, on detecting a wet or thoroughly wet control circuit, generates a signal which is intended to prevent unintentional lifting or lowering of the vehicle window.